There have been known a variety of ink-jet recording devices in which a number of ink droplets are ejected in response to an image signal and then deposited onto a recording medium such as plain paper to reproduce a visible image corresponding to the image signal. To reproduce as many images as possible in a relatively short span of time and to provide the resultant images with an elevated quality, it has been understood that it is effective to change diameter of ink dots to provide the resultant image with a tone gradation.
For this purpose, an amount or volume of ink material to be ejected from nozzles must be controlled in accordance with the tone gradation. Thus, in the past, it has been proposed an ink-jet recording device in which a plurality of ink-jet heads are incorporated. In this recording device, a diameter of the nozzle in one ink-jet head is determined to have a different size from that of another ink-jet head, enabling the device to eject different sizes of ink droplets.
The technique is useful to some extent, however, it cannot significantly expand the gradation range and, therefore, a sufficient tone gradation required for printing a picture-like halftone image with a smooth change could not be achieved.